Newcastle fowl disease (pseudoplague, atypic plague, Asian plague, avain pneumoencephalitis) is a virus acute infection disease occurring in the form of epizootia and causing mass death of perceptible fowl. Newcastle fowl disease is the most widespread infection throughout the globe; it brings about a high economic damage to the national economies and pertains to dangerous infections. Control of Newcastle fowl disease is an urgent and important portion of the program of the fight against infectional diseases of animals and fowl.
At the present time, the foci of infection of Newcastle fowl disease are eliminated by the total slaughter of ill and suspected fowl.
Known in the art are various inactivated and virus-vaccines for specific prophylaxis of Newcastle fowl disease. Inactivated vaccines are prepared by inactivation of a virus-containing extra-embryonic liquid with formalin or betapropiolactone. The basic disadvantages thereof reside in a low immunogeneity, high production costs and the necessity of individual treatment of fowl by injection.
Known are virus-vaccines employed for specific prophylaxis of Newcastle fowl disease which are classified into two groups: lentogenic avirulent (strains B.sub.1, La-Sota, F) and mesogenous with the residual virulence (strains Roakin, Komarova, H). Dry virus-vaccines consist of a virus-containing extra-embryonic liquid and a protective medium. As the protective medium use is made mainly of defatted milk ("Partial Veterinary Virusology", Moscow, "Kolos" Publishing House, p. 233-240).
The main disadvantage of the virus-vaccine pertaining to the group of mesogenous strains is the presence of a residual virulence, wherefore they have a limited application. Virus-vaccines of strains "B.sub.1 " and "F" are weakly immunogenic, while the vaccine of the strain "H" have a residual reactogeneity for fowl.
Among currently known vaccines, the most pronounced immunogeneity is inherent in the vaccine of the strain "La-Sota". This vaccine consists of 50% of virus-containing extra-embryonic liquid of the strain "La-Sota", 50% of the protective medium and antibiotics. The vaccine of the strain "La-Sota" is harmless; when administered intranasally, it is used in the volume of 0.1 ml at the dilution of 1:25; at enteral administration with potable water for two days in a volume of 5 to 15 ml at the dilution of 1:500; at aerosol administration in doses of 600 to 1,200 EID.sub.50.
The method for preparing vaccine from the strain "La-Sota" consists in the following: chicken embryos are infected with the virus in the volume of 0.1 ml at the dilution of 10.sup.-3, matrass breeding of the virus with an activity of at least 10.sup.7.5 EID.sub.50 /ml is effected for 96-120 hours, then the recovered virus-containing extra-embryonic liquid is mixed with the protective medium, packed, lyophilized and the final vaccine is checked. This vaccine for the prophylaxis purposes is used, as it has been mentioned hereinabove, intranasally, as aerosol, and enterally with potable water. However, the use of the vaccine is effected repeatedly. Thus, fowl of an up to 150 days' age is vaccinated with this virus-vaccine three times and then every 6 months. Despite repeated vaccination with this vaccine, in numerous fowl-breeding farms there occur breakage of immunity and fowl death because of Newcastle disease.